1. Field of the Invention
The present invention relates to optical systems. More specifically, the present invention relates to solid-state lasers.
2. Description of the Related Art
Weapon-class lasers are required to have the highest possible power per weight ratio in order to fulfill requirements for a variety of airborne and ground tactical applications. The implementation of a high-energy weapon-class laser system is currently limited to large platforms due to the relatively low power per weight ratio numbers in the present approaches.
Prior attempts to implement a weapons class laser range from the chemical laser to the diode-pumped solid-state power oscillator (PO). The chemical laser is a highly complex system and typically takes up a good portion of the available real estate in an aircraft. In addition, the chemical handling makes this an extremely cumbersome and undesirable approach. The relatively clean diode-pumped solid-state laser approach is much more desirable.
Solid-state lasers, however, have their share of problems. These devices typically require active (or passive) phase conjugation techniques to compensate for high beam distortion generated as the laser propagates through the amplifier chain. In addition, the gain elements themselves are currently comprised of complex, composite slabs that are very expensive and prone to damage. Large size solid-state laser active media are required for power/energy scaling of laser systems, but such media is difficult to fabricate. The number of potential materials for the gain medium is also reduced, since some materials cannot be grown to the sizes needed for a high-energy laser. Furthermore, the large size of the gain medium makes it harder for thermal management to extract heat out of the medium. The large gain medium also makes it more difficult to control optical uniformity, making it harder to control laser beam quality. Finally, the MOPA approach limits the ultimate optical (and, therefore, the overall) conversion efficiency, which results in increased power and wastes heat extraction real estate.
One high-energy solid-state PO laser is the multiple disk heat capacity laser. This laser uses multiple disks of smaller size gain media instead of a single, large bulk medium. Thermal management, however, remains a problem for this approach. The laser can only operate for a few seconds before it needs to be cooled. The smaller gain media disks are faster to cool than a single bulk medium, but several minutes could still be needed for cooling before the laser can be reactivated. In addition, pumping for the multiple disk laser can be difficult to arrange.
Another solid-state approach is the fiber laser. Fiber lasers have inherently high efficiencies because they allow for 100% pump power absorption and operate at very high laser intensity, and can be cooled efficiently due to their inherently high surface to volume ratio. Fiber lasers, however, are ultimately limited by the maximum power at which they can operate due to intensity damage threshold limits. In order to generate higher powers, several fibers need to be combined. This, however, requires phasing of multiple fiber oscillators, which adds a number of problems (not satisfactorily solved yet) and associated complexities.
Hence, a need exists in the art for an improved solid-state laser that is scalable for high energy and power, and that offers better optical quality, easier fabrication, and improved thermal management than conventional approaches.